Heating element



Aug. 13, `1968 .vvy M R. L.. CASPER ET Al.

HEATING ELEMENT Filed Dec. 1. 1.966

lFig. 2

INVENTOR.

RICHARD L. CASPER FRANK J. BAUMEISTER United States Patent O 3,397,375HEATING ELEMENT Richard L. Casper, Grand Island, and Frank J.Baumeister, Lockport, N.Y., assignors to The Carborundum Company,Niagara Falls., N.Y., a corporation of Delaware Filed Dec. 1, 1966, Ser.No. 598,455 7 Claims. (Cl. 338-330) ABSTRACT F THE DISCLOSURE Anelectric heating element comprising a tubular resistance body having ahot zone section and a cold end terminal section engageable with anelectrical contact. A ceramic bulk fiber `filler is disposed within acontrolled portion of the cold end terminal section to impede the flowof radiative heat toward the electrical contact area.

This invention relates -to heating elements and, more particularly, toterminal -assemblies used on high temperature heating elements.

One of the critical problems encountered in the utilization of heatingelements is that :excessive temperatures due to thermal conductivityoccurring in the electrical contact area and the inside diameter of theelement a-djacent the terminal portion result in the fracturing and/orburning up of these portions causing premature failure of the heatingelements.

The general purpose of the present invention is to provide a solution tothe above problem by providing a new and improved terminal assembly fora heating element which permits the terminal contact .area to operate atcooler temperatures to materially increase the useful life of theheating element.

It -is therefore an object of the present invention to provide a new andimproved heating element.

lt -is 'another object of the present invention to provide .ia new andimproved heating element having a novel terminal assembly.

It is a further object of the present invention to provide a new andimproved heating element having a novel terminal assembly which isdurable, rugged, and simple in construction.

It is still another object of the presen-t invention to provide a newand improved heating element having a novel terminal assembly whichmaintains the electrical contact area at relatively cool temperatures.

It is still a further object of the present invention to provide a newand improved heating element having an insulating filled disposed withinthe body of the element at the electrical contact area thereof.

These and other objects of the present invention will become moreapparent upon consideration of the foll-owing detailed descriptionthereof when taken in conjunction with the following drawings, inwhi-ch:

FIG. 1 is a top plan View of the heating element constrncted inaccord-ance with the principles of this invention;

FIG. 2 is an end elevational view of the heating element of FIG. l; and

FIG. 3 is a fragmentary sectional View of a furnace illustrating theheating element of the present invention installed therein.

Referring to the drawings in detail, -it will be seen that an electriclresistance heating element constructed in accordance with theprinciples of this invention comprises an elongated, hollow, tubularresist-ance body, generally designated 10, having a hot zone section 12of a double spiral configuration, an end portion 14, and a split coldend terminal section 16. Resistance body is preferably composed of anonmetallic resistance material such Ias very dense, high-purity,self-bonded silicon carbide.

The split cold end terminal section 16 comprises a pair of laterallyspace-d, elongated members or legs 18 and 20 of substantiallysemicircular, trough shaped cross sections (FIG. 2), forming asubstantially hollow, tubular chamber :and defining a pair ofdiametrically opposed slots 22 and 24. Disposed in slots 22 and 24adjacent an end portion 26 of resistance body 10 are a pair of elongatedinserts or shims 28 and 30, respectively, which function as primarybraces and insulators between legs 18 and 20. Although the shims arepreferably formed of alumina, it should be appreciated that theprinciples of this invention contemplate the use of any Istronginsulating ceramic material in lieu of alumina, if desi-red. v

A ceramic bulk fiber filler 32, preferably of short staple, is providedto fill a controlled portion of the inside dianiet-er of the resistancebody 10 in order to impede the flow of radiative heat in a directiontoward end portion 26, thus maintaining the terminal area relativelycool. Moreover, the bulk fiber functions as a secondary brace betweenlegs 18 and 20 to preclude an electrical short therebetween.

Means are provided for urging members 18 and 20 against shims 28 and 30,such means comprising a collar 34, preferably composed of a ceramicmaterial and formed of four arcuate shaped members 36 having their innersurfaces, respectively, conforming to the outer cylindrical surface ofresistance body 10. Also, collar 34 aids in securing the bulk fiberfiller 32 in place and retaining the heating element in the heatingchamber of a furnace. As shown in FIG. 2, members 36 arecircumferentially spaced from each other to form openings foraccommodating the yshims 28 and 30. A clamp 42`is provided for hol-dingmembers 36 in engagement with resistance body 10. If desired, only twosubstantially semi-circular members may be substituted for the fourmembers 36 that constitute collar 34 within the purview of the presentinvention.

A coating of any suitable electrical conducting material `44, such asaluminum by way of example, is deposited on the exterior surface loflegs 18 and 20 `adjacent end portion 26 (FIG. l) in order to provideterminals for the resistance body 10. The coating may be sprayed ontolegs 18 and 20 or it may be applied in any conventional mannerwell-known in the art.

End portion 26 of resistance body 10 is adapted to be mounted within asplit clip type of contact 46 comprising a pair of resilient metallictongs 48 and 50 having arcuate shaped portions 52 and 54 respectively,conforming to the louter cylindrical surfaces of legs 18 and 20. Theclip 46 is composed of any suitable metal such as stainless steel or ahigh chrome, nickel base, heat resistant alloy for example, and may have-the inner surfaces of tongs 48 and 50 sprayed with a suitableelectrical conducting material, if desired. The bottom of clip 46 iselectrically and mechanically secured to a pair of electricallyconducting terminal straps 56 and 58 and mounted on la base 60, composedof a suitable insulating material, by means of bolt and nut combinations62, respectively.

One manner of installing the heating element of the present `inventionis exemplified in FIG. 3 which shows the heating element protruding intothe side wall 64 of a high temperature electric furnace, Normally, aterminal tube 68, formed `of a suitable high dielectric insulatingmaterial, is snugly fitted `into a bore 69 of the furnace and envelopesa portion of the resistance body 10 to preclude the possible shorting ofthe terminal ends caused by the full element voltage which exists alongthe entire length of the terminal. Resistance body 10 is loosely fittedinto the terminal tube 68 (shown exaggerated in FIG. 3) in Iorder tofacilitate the replacement of the heating element in a furnaceinstallation. The terminal tube 68 is provided with a flange 70 abuttingagainst the exterior surface of the furnace wall and the collar 34 ofthe heating element is disposed flush against the flange 70. It shouldbe appreciated that collar 34 may be formed integral with the terminaltube 68, if desired, w-ithin the scope of the present invention.

As a result of the present linvention, a new and improved heating`element is provided having a novel terminal assembly for minimizingheat radiation in the electrical cont-act area. By the provision fo aceramic collar, the heating element is held together and in place in afurnace installation and the electrical contact area is disposedexteriorly olf the furnace walls. Moreover, the element can be mountedto hang vertically downwardly from the roof of a furnace or project upthrough the bott-om of a furnace chamber. In lthe latter case, however,auxiliary support means would tbe necessary to maintain the element inan upright position.

Another :advantage residing in the device of the present invention isthe provision of a thermal insulating ceramic bulk fiber ii-ller lwithina vcontrolled portion of the inside ydiameter of the resistance body forpreventing heat flow toward the electrical contact area.

A preferred embodiment of this invention having been described andillustrated, it is to be -realized that modifications thereof may bemade without departing from the broad spirit and scope of this inventionas defined in the appended claims.

I claim:

1. A heating element comprising: an elongated resistance body having ahot zone section and a cold end section; said cold end sectioncomprising a pair of laterally spaced elongated members having outersurfaces, respectively; a coat-ing of electrical conducting materialdeposited on said outer surfaces of said elongated members adjacent theends thereof remote from said hot zone section; and insulating lillercomposed of a ceramic bulk fiber disposed between said laterally spacedelongated memlbers along a controlled portion thereof.

2. A heating element as dened in Iclaim 1 including a pair of insulatingshims disposed between said laterally spaced elongated members.

3. A heating element as defined in claim 2 including means disposedabout said laterally spaced elongated members for urging said membersagainst said insulating shims.

4. A heating element as defined in claim 3 -in which said urging meanscomprises a collar formed of a plurality of elements, and a clamppositioned about said plurality of elements.

5. A heating element as `defined in claim 4 in which said lends of saidelongated members remote from said hot zone section are engageable withan electrical contact.

v6. A heating element as defined in claim 5 in which said laterallyspaced elongated members are substantially semiicircullar vin crosssection, respectively, and dene a hollow chamber for receiving saidfiller material.

7. A heating element as defined in claim 6 in which said elongatedresistance body is composed of dense, selfbonded silicon carbide.

References Cited UNITED STATES PATENTS 3,307,136 2/1967 Fitz/er et al338--330 X 3,3 3 6,431 8/ 1967 Biddulph 13--25 FOREIGN PATENTS 838,917 f6/1920 Great Britain.

LARAMIE E. ASKIN, Primary Examiner.

E. GOLDBERG, Assistant Examiner.

